Method for converting hydrocarbons



Feb- 25 1969 N. M. HALLMAN METHOD FOR CONVERTING HYDROCARBONS Filed Aug. l. 1966 United States Patent O 9 Claims ABSTRACT OF THE DISCLOSURE Method for achieving thermal balance within a catalytic hydrocracking process whereby the effluent from the hydrocracking reaction is cooled by the generation of steam and the steam so generated is utilized to drive condensing turbines for the movement of the process hydrocarbons through the hydrocracking system.

This invention relates to a method for converting hydrocarbons into lower boiling hydrocarbon conversion products. It particularly relates to a catalytic hydrocracking method for converting hydrocarbons into lower molecular weight products. It specifically relates to an improved method for achieving thermal balance within a catalytic hydrocracking process.

Hydrocracking, or destructive hydrogenation, as distinguished from relatively simple addition of hydrogen to unsaturated bonds between carbon atoms, effects definite changes in the molecular structure of hydrocarbons. It produces from a relatively heavy hydrocarbon feedstock relatively light or lower molecular weight hydrocarbon products. For example, the hydrocracking reaction can convert a petroleum feedstock, such as gas oil, almost completely into gasoline boiling range products and lighter. It is of significant commercial interest since hydrocracking offers unique advantages over conventional catalytic cracking operations. Therefore, hydrocracking may be designated as a conversion process wherein not only are lower molecular weight or lo'wer boiling conversion products produced, but these conversion products are substantially more saturated than when hydrogen or hydrogen-donor material is not present.

Although many of the prior art processes relating to the hydrocracking function may be and are conducted on a strictly thermal basis, the preferred processing technique involves the utilization of a catalytic mass possessing a high degree of hydrocracking activity. By the use of proper catalysis, the hydrocracking reaction can selectively convert a wide variety of feedstocks to lower boiling distillates with significantly less coke and gas yield and with higher yields of quality liquid products than are usually produced by conventional catalytic cracking processes performed in the substantial absence of hydrogen or hydrogen-donor material.

It has been noted that much of the effort on the part of the prior art has been to develop processing schemes and manufacturing methods to increase the selectivity of the catalytic mass used for the hydrocracking reaction. However, even though this reaction is known to be strongly exothermic in nature, eg. 200 to 400 B.t.u.s per pound of feed hydrocarbon converted, there has only been a small effort on the part of the prior art to improve on the utility and capital costs for a conventional hydrocracking process.

Therefore, it is an object of this invention to provide a method for converting a hydrocarbon feedstock into lower boiling hydrocarbons. It is another object of this invention to provide an improved method for converting hydrocarbons into lower boiling hydrocarbon conversion products via exothermic chemical reaction with hydrogen.

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It is a particular object of this invention to provide an improved method for achieving thermal balance within a catalytic hydrocracking process.

These and other objects will be achieved by the invention particularly described hereinbelow and illustrated by reference to the appended drawing which is a schematic flow diagram of one specific embodiment of the invention.

According to the present invention, a method for converting hydrocarbons by exothermic chemical reaction with hydrogen in a conversion zone comprises passing the hydrocarbon by first pumping means into indirect heat exchange with the reaction eluent from the conversion zone sufficient to preheat the hydrocarbons as hereinafter specified; subjecting said heated hydrocarbons at reaction temperature to catalytic exothermic conversion in the presence of hydrogen and conversion catalyst; withdrawing from said zone at a temperature of at least reaction temperature reaction efliuent containing the conversion products and unreacted hydrogen; cooling said effluent to a temperautre below reaction temperature by means comprising preheating said hydrocarbons by indirect heat exchange with the hydrocarbons, as specified, and generating steam by indirect heat exchange with water in a steam generation zone; passing the cooled efiiuent into a separation zone wherein a liquid conversion product stream and a hydrogen gas stream, including unreacted hydrogen, are formed; removing said conversion product stream and said hydrogen stream from the separation zone; recycling the removed hydrogen gas stream by second pumping means to the conversion zone; and, passing generated steam into condensing turbine drive means under conditions sufficient to drive said second pumping means connected thereto.

A more particular embodiment ofthis invention includes the recycling of the condensate from turbine drive means to the steam generation zone as at least part of the water required for steam generation.

A still further specific embodiment of this invention includes the passing of substantially all of said generated steam into prime movers integrally associated with said method for operation thereby, and the passing of said removed conversion product stream into power recovery turbine means connected to said first pumping means.

As used herein, the term reaction temperature is intended to encompass that temperature chosen by the operator to achieve conversion. Preferably, it is the feed inlet temperature to the reactor in question, but this invention is not to be limited thereto.

It can be seen from the above description of the present invention that the basic concept of the invention is 'based upon the discovery that the exothermic heat of reaction can be recovered in an economical and novel manner and used to support substantially all of the auxiliary and ancillary prime movers necessary for the practice of the method. In other words, it was discovered that the method for converting hydrocarbons could be operated in substantially thermal balance without the use of significant amounts of added heat from an extraneous source.

As mentioned previously, those skilled in theart recognize that the hydrocracking reaction is substantially exothermic in nature. Therefore, the heat generated by the reaction must be removed in a controlled manner if selective hydrocracking is to be achieved. Most of the prior art processes utilize plural stage conversion zones in order to prevent the temperature rise within any one stage from exceeding the tolerable temperature limits on materials of construction used on the reactors. Consequently, a quenching medium, such as relatively cold hydrogen-containing gas, is injected in physical Iadmixture with the reactor efiiuent in order to absorb the excess heat of reaction prior to the next stage of the reaction. However, the injection method does not to any considerable extent recover the excess heat of reaction for use within the process. Accordingly, ineliiciencies are inherent in the prior art methods of operating the hydrocracking process.

Suitable hydrocarbon charge stocks for the practice of the present invention include kerosene fractions, gas oil fractions, lubricating oil and white oil stocks, heavy cycle stocks, fuel oil stocks, reduced crudes, various high boiling bottoms fractions including vacuum residuum and other sources of hydrocarbons having a depreciated market demand due to the relatively high boiling points of these charge stocks, accompanied by the usual presence of `asphaltic and other heavy residues. The present invention is particularly directed toward processing the heavier of the aforementioned hydrocarbon feedstocks, namely vacuum gas oil fractions, heavy cycle stocks, reduced crudes, etc.; that is, those hydrocarbons having an initial boiling point in excess of about 650 F., preferably having an ASTM boiling range from 650 F. to about 1,l00 F. Generally, al1 of the sources of hydrocarbon feedstocks containing nitrogenous compounds, and it is distinctly preferable for the practice of this invention to limit the nitrogen content of the hydrocarbon feedstock to less than 1500 ppm. total nitrogen.

The catalyst used in the practice of the present invention may be any hydrocracking catalyst known to those skilled in the art as being selective for the hydrocracking reaction in the presence of nitrogenous compounds, such as ammonia. Thus, in regard to nitrogen-insensitive hydrocracking catalyst, the term metallic component or catalytically active metallic component is intended to encompass those catalytic components which are employed for their hydrocracking activity or for their propensity for the destructive removal of the nitrogenous compounds, aS the case may be. These catalytically active metallic components are selected from the metals and compounds of Groups VI-A and VIII of the Periodic Table. In this manner, the metallic catalytic components are distinguished from those components that are employed as the solid support, or carrier material, or the acidic cracking component. The metallic component of the catalyst which may be employed in the practice of this invention may comprise two or more of such metals. Thus, the catalyst employed in the present method may comprise chromium, molybdenum, tungsten, iron, cobalt, nickel, palladium, platinum, ruthenium, rhodium, osmium, iridium, and mixtures of two or more including nickel-molybdenum, nickel-chromium, molybdenum-palladium, molybdenum-platinum, cobalt-nickel-molybdenum, chromium-platinum, chromium-palladium, molybdenum-nickel-palladium, etc.

As hereinafter set forth in greater detail with respect to the embodiment of the present invention represented by the appended drawing, the method of the present invention may be composed of a single reaction stage or of two or more separate but integral reaction stages representing a plural ystage conversion zone containing catalyst. If a plural stage conversion zone is used, each stage may contain a distinct catalytic composite of the same composition in each stage, or of a different composition in each stage, or any combination and mixtures of catalyst depending upon the needs of the business situation experienced by those skilled in the art.

Regardless of the particular catalytically active component or components, these are composited with a suitable solid carrier material which may be either naturally occurring or which may be synthetically prepared by means known to those in the art. Naturally occurring carrier materials include various aluminum silicates, particularly when acid-treated to increase the activity thereof, -various aluminacontaining clays, sands, earths and the like. Typically, the synthetically prepared components include at least a portion of both silica and aluminum. Other suitable carrier material components which may, in particular instances, be combined as an integral portion of the hydrocracking catalyst include zirconia, magnesia, thoria, boria, titania, strontia, hafnia, etc., with the preferred cracking component consisting essentially of the composite of silica and alumina.

Since the various embodiments of the present invention utilize 4hydrocarbon feedstocks generally containing nitrogenous compounds, it is preferable to practice the present invention in combination with a hydroning step which converts the nitrogenous compounds into ammonia. However, neither this combination nor the hydroning step forms any part, per se, of this invention. By operating in this preferred manner, the ammonia formed can be easily removed from the linal reaction product from the conversion zone by, say, Water washing, thereby leaving a product of lower boiling hydrocarbons which are substantially free from nitrogenous compounds. If a hydroning operation is to be conducted in conjunction with the present invention, it may be performed either adiabatically or isothermally, and generally is practiced at a temperature from 600 F. to 850 F., preferably from 650 F. to 750 F.; a pressure from 500 to 3,0000 p.s.i.g., preferably from 800 to 2,000 p.s.i.g.; liquid hourly space velocity (LHSV) from 0.5 to 10, preferably from 1 to 5; and a hydrogen-to-oil ratio from 500 to 20,000 s.c.f./b., preferably from 1,000 to 10,000 s.c.f./b. The hydroiining catalyst typically m=ay be a conventional cobalt-molybdena on a silica-alumina base. Those skilled in the art know how to suitably adjust these conditions in order to convert at least part of the total nitrogen present to arnmonia without substantial conversion of the feedstock hydrocarbons to lower boiling hydrocarbons.

Referring now to the drawing, the hydrocarbon charge stock enters the process from line 10 and is pumped by rst pumping means 11 into line 12 wherein it is admixed with hydrogen which is introduced by recycle via line 30. For purposes of illustration, the hydrocarbon feedstock may have an ASTM boiling range from an initial boiling point of 650 F. to 1,100 F. However, the hydrocarbon charge in line 10 is not intended to be limited thereto.

The mixture of hydrogen and hydrocarbon in line 12 is passed into exchanger 13 such that the temperature of the mixture is increased, for example, from F. to 380 F. Typically, the hydrogen is present in an amount within the range of from 500 to 30,000 standard cubic feet per liquid barrel of charge, e.g. 20,000 s.c.f./ b. The preheated mixture is then raised to about 760 F. by indirect heat exchange with the iinal reaction effluent in exchanger 16 and is passed through line 17 into -hydrocr-acking reactor 20. If desired, recycle stock and/or hydrogen ygas may be introduced into the feed to reactor 20 via line 19. Also, the mixture of hydrogen and feed hydrocarbons in line 17 are preferably heated to reaction temperature of, say, 830 F., by passing through la conventional lired heater not shown.

The precise operating conditions in reactor 20 will be dependent upon the various physical and/or chemical characteristics of the particular hydrocarbons being processed, and will be dependent upon the type of catalyst 18 contained within reactor 20. In any event, reactor 20 will be maintained at a conversion temperature of from 650 F. to 900 F., preferably .about 830 F., and under an imposed pressure within the range of from 300 to 3,000 p.s.i.g., preferably about 2,200 p.s.i.g. Higher pressures appear to favor the destructive removal of any remaining nitrogenous compounds as Well as the conversion of those hydrocarbons boiling in excess of about 650 F. The total hydrocarbons in the feedstock in reactor 20 will contact the particular catalyst 18 at a liquid hourly space velocity within the range of about 0.5 to about 10, preferably labout 0.75.

The catalyst deposed wit-hin the catalyst bed 18 serves a dual function: that is, the catalyst is non-sensitive to the presence of nitrogenous compounds, while at the same time it is capable of effecting the destructive removal thereof, and also is capable of effecting conversion of 'at least a portion of those hydrocarbons boiling, for example, at a temperature in excess of about 650 F. to 700 F. Generally, the process conditions are adjusted in reactor to provide about 20% to 60% by volume conversion of the feedstock hydrocarbons to lower boiling hydrocarbons per pass. Generally, the chemical hydrogen consumption for this reaction will range from about 500 to 5,000 s.c.f./b. of feed hydrocarbons.

Since the hydrocracking reaction is exothermic in nature, the reaction eflluent from reactor 20 is withdrawn at a temperature of at least conversion temperature, and typically is substantially above the conversion temperature, eg. 880 F., through line 21 and passed into exchanger 16 wherein the reactor 20 efiuent is quenched to a temperature below the conversion temperature maintained in reactor 20, to wit: about 52.0 F., by indirect heat exchange with the feed hydrocarbons as hereinabove discussed. The quenched effluent stream is now passed via line 22 from exchanger 16 into steam generator 23 wherein, for example, saturated steam at 250 pounds is generated. The cooled effluent stream is withdrawn from steam generator 23 at a temperature of about 455 F. and passed into heat exchanger 13 wherein it is further cooled to a temperature of about 300 F. by indirect heat exchange with the feed hydrocarbons as hereinabove discussed. The cooled effluent stream is admixed with additional hydrogen from line 15, if desired, and passed from exchanger 13 via line 25 into separator 26.

ln separator 26 the hydrogen-containing gas, including unreacted hydrogen, is removed via line 28 and compressed by second pumping means 29 to an elevated pressure for recycle via line 30 in admixture with the feed hydrocarbons in line 12 as hereinabove discussed.

The normally liquid products are removed from separator 26 via line 27 and passed into power recovery turbine means 31 wherein at least part of the power required to drive pumping means 11 is effected. The desired lower boiling hydrocarbons are removed to storage or other processing means via line 32.

Referring again to steam generator 23, the generated steam is passed via line 33 and split into, for example, two portions for driving prime movers integrally associated with the method. A first portion is passed via line 34 into condensing turbine drive means 35 under conditions suicient to drive pumping means 29 connected thereto as discussed hereinabove. Another portion of the generated steam is passed via line into other condensing turbine drive means 41 under conditions suilcient to supply the remaining power requirements to drive the first pumping means 11 connected thereto. It is noted at this point that the rst pumping means 11 is driven by a combination of the power train derived from condensing turbine 41 and power recovering turbine 31 both appropriately connected to the `iirst pumping means 11. If desired, the generated steam in line 33 may be superheated by means not shown to eiectuate additional eiciencies in the condensing turbine drive means illustrated.

The steam condensate from condensing turbine 41 is removed via line 42, admixed with the condensate from condensing turbine 3S from line 36 and line 37, and passed into condensate separator 38. A minor proportion of vent gas is removed from separator 38 by means not shown. The condensate water is passed from separator 38 via line 39 to steam generator 23 as at least part of the water required to generate the steam. Additional feed water, as needed or desired, can be added to the system via line 43.

As illustrated hereinabove, the steam generator 23 is located in bet-Ween exchangers 16 and 13 respectively on the direction of reaction eluent ow from reactor 20. However, it is not intended that the present invention be limited to such an arrangement. Those skilled in the art and the design of the hydrocracking process utilizing the concepts described herein, can place the steam generator before the heat exchanger train, after the heat exchanger train, in between independent stages of a plural stage conversion process, or any other process location as long as the heat of reaction is substantially recovered by steam generation which is used to drive prime movers integrally associated with the method.

Thus, from the illustrative embodiment given hereinabove, it can be seen that the present invention recovers to an optimum extent the exothermic heat of reaction generated by the hydrocracking reaction via means including steam generation for driving prime movers integrally associated 'with the method, and via means for recovering the potential energy contained in the high pressure reaction effluent using power recovery turbine drive means to drive prime movers integrally associated with the method.

EXAMPLE The practice of the present invention is further illustrated by the following example 'which indicates the products that may be obtained from the processing of a vacuum gas oil stream according to the scheme shown in the appended drawing and using typical conditions cited hereinabove. The feedstock hydrocarbons had an API gravity of 23.1, a sulfur content of about 1.5 wt. percent, a nitrogen content of about 1200 ppm. by Weight, and an ASTM boiling range of from 660 F. to 1100 F. The hydrogen purity was 97.5 mol percent. The following products "were obtained on the basis of charging 26,000 barrels per stream day of the feedstock:

API BPSD The invention claimed is:

1. Method for converting hydrocarbons by exothermic chemical reaction with hydrogen in a conversion zone which comprises:

(ya) passing the hydrocarbons by first pumping means into indirect heat exchange with the reaction effluent from the conversion zone suicient to preheat the hydrocarbons as hereinafter specied;

(b) subjecting said heated hydrocarbons at reaction temperature to catalytic exothermic yconversion in the presence of hydrogen and conversion catalyst;

(c) ywithdraiwing from said zone at a temperature of at least reaction temperature, reaction efuent containing the conversion products and unreacted hydrogen;

(d) cooling said effluent to a temperature below reaction temperature by means comprising (i) preheating said hydrocarbons by indirect heat exchange with the hydrocarbons as specified, and

(ii) generating steam by indirect heat exchange with water in a steam generation Zone;

(e) passing the cooled euent into a separation zone wherein a liquid conversion product stream and a hydrogen gas stream, including unreacted hydrogen, are formed;

(f) removing said conversion product stream and said hydrogen stream from the separation zone;

(g) recycling the removed hydrogen gas stream by second pumping means to the conversion zone; and

(h) passing generated steam into condensing turbine drive means under condition's suicient to drive said second pumping means connected thereto.

2. Method according to claim 1 wherein condensate from said turbine drive means is recycled to said steam generation zone as at least part of said fwater.

3. Method according to claim 1 wherein said generated steam is lsuperheated prior to passing into said turbine drive means.

4. Method according to claim 1 wherein hydrocarbons boiling 'within the range of 650 F. to 1100 F. are converted under hydrocracking conditions to lower boiling hydrocarbon conversion products.

5. Method according to claim 4 :wherein said reaction temperature is from 625 F. to 900 F. and said reaction euent is withdrawn at a temperature substantially in excess of said reaction temperature.

6. Method according to claim 5 wherein generated steam is passed to second condensing turbine drive means under conditions sucient to at least partly drive said ttirst pumping means.

7. Method according to claim 6 wherein 'said generated steam is superheated prior to passing into said turbine drive means.

8. Method according to claim 6 wherein condensate from said condensing turbine drive means is recycled to said steam generation zone as at least part of said water.

9. Method according to claim 6 wherein substantially al1 of said generated steam is passed into prime movers, integrally associated with said method, for operation thereby, and said removed conversion product stream is passed into power recovery turbine means connected to said rst pumping means.

References Cited UNITED STATES PATENTS 1,951,792 3/1934 Harding 208-108 2,491,303 12/ 1949 Eastman 208-146 2,953,521 9/1964 Bowles 208-108 3,329,605 7/ 1967 Tokuhisa et al. 208-130 DELBERT E. GANTZ, Primary Examiner.

T. H. YOUNG, Assistant Examiner. 

